Previous research has shown that fathers taking some time off work around childbirth, especially periods of leave of 2 or more weeks, are more likely to be involved in childcare related activities than fathers who do not do so. Furthermore, evidence suggests that children with fathers who are ‘more involved' perform better during the early years than their peers with less involved fathers. This paperanalyses data of four OECD countries - Australia; Denmark; United Kingdom; United States - to describe how leave policies may influence father's behaviours when children are young and whether their involvement translates into positive child cognitive and behavioural outcomes. This analysis shows that fathers' leave, father's involvement and child development are related. Fathers who take leave, especially those taking two weeks or more, are more likely to carry out childcare related activities when children are young. This study finds some evidence that children with highly involved fathers tend to perform better in terms of cognitive test scores. Evidence on the association between fathers' involvement and behavioural outcomes was however weak. When data on different types of childcare activities was available, results suggest that the kind of involvement matters. These results suggest that what matters is the quality and not the quantity of father-child interactions.